Multi Constellation GNSS PPP for Climate Dynamics: Convergence Performance of Geodetic and Low-cost GNSS Receivers

Global Navigation Satellite Systems (GNSS) are widely used to monitor climate dynamics, understand environmental processes, and assess climate impacts. GNSS observations contribute to a wide range of applications, including monitoring glacier dynamics in polar regions, detecting sea-level change, supporting UAV-based glacier mapping with GNSS static positioning, and investigating heavy precipitation and flood events, etc.

Relative positioning requires additional receivers, which impose significant logistical constraints in harsh environments. Conversely, Precise Point Positioning (PPP) enables high-accuracy solutions without reference stations, thereby offering substantial operational advantages. Concurrently, GNSS hardware has also evolved, and in recent years, low-cost (OEM) GNSS receivers have become an integral part of such applications due to their low-cost, low-power consumption, and lightweight design compared to geodetic systems.

PPP is commonly carried out using online services such as the CSRS-PPP service. Following the recent integration of the Galileo constellation, the system has been updated. However, multi-GNSS PPP convergence studies under this configuration remain limited. Therefore, this study aims to evaluate the convergence performance of positioning system combinations and to assess the performance of low-cost GNSS receivers compared with geodetic systems.

In this study, GNSS data covering 15 days in the last quarter of 2025 were analyzed. Observations from the International GNSS Service (IGS) station ISTA were evaluated together with data from a low-cost GNSS receiver (Mosaic-X5) installed approximately 55 m away. PPP processing was performed in static mode using GPS (G), GPS+GLONASS (GR), and GPS+GLONASS+Galileo (GRE) configurations via the CSRS-PPP service. Convergence times in horizontal and vertical components were assessed at 95% confidence levels for accuracy thresholds of 15 cm, 10 cm, and 5 cm.

The results indicate that the difference in average convergence time between geodetic and low-cost receivers does not exceed 2 minutes for all configurations. The use of the GRE configuration reduces convergence time by 42%, 37%, and 36% in the horizontal component and by 29%, 30%, and 36% in the vertical component, compared to GPS-only. These findings demonstrate that multi-constellation GNSS significantly improves PPP convergence performance, while low-cost receivers yield results comparable to geodetic systems.